Situation: A 46-year-old man with primary adrenal insufficiency (Addison disease) is brought to the emergency department after 2 days of vomiting and diarrhea. He usually takes hydrocortisone 15 mg every morning and 5 mg every afternoon, and fludrocortisone 0.1 mg daily. He was treated for pulmonary tuberculosis 5 years ago. He recovers and returns to his usual doses. His written sick-day plan says: during a fever of 38 °C (100.4 °F) or higher, double each usual hydrocortisone dose until the fever has settled. A month later he calls at 06:00, before his morning dose, because he has had a fever of 38.3 °C (100.9 °F) with a cough since waking. He is eating and drinking and has not vomited. Assume his fever is still present when his afternoon dose is due. What total amount of hydrocortisone should he take today?

His usual daily hydrocortisone is 15 mg + 5 mg = 20 mg. The plan doubles each dose during fever of 38 °C or higher, so he takes 30 mg in the morning and 10 mg in the afternoon, a total of 40 mg. Fludrocortisone is not changed by these rules.

Core calculation
This patient’s usual daily hydrocortisone requirement is 20 mg, given as 15 mg in the morning and 5 mg in the afternoon. His individualized sick-day plan instructs him to double each hydrocortisone dose when his temperature reaches 38 °C (100.4 °F) or higher. Because his current temperature is 38.3 °C (100.9 °F), the rule applies to both scheduled doses today.

The morning dose becomes 30 mg and the afternoon dose becomes 10 mg, for a total of 40 mg. The fludrocortisone dose remains unchanged at 0.1 mg daily because mineralocorticoid replacement is not adjusted under a short-term fever rule.

The key principle is that each hydrocortisone dose is doubled individually, not the total daily dose as a single calculation. Doubling the usual daily total of 20 mg would also produce 40 mg, but the plan specifies doubling each dose to preserve the normal circadian pattern of cortisol replacement.

Watch out! The patient is eating, drinking, and not vomiting, so this is a sick-day adjustment rather than an adrenal crisis. Parenteral hydrocortisone or emergency injection is not indicated at this point.

Why fever triggers dose adjustment
In primary adrenal insufficiency, the adrenal cortex cannot increase endogenous cortisol production in response to physiological stress. Fever, infection, vomiting, diarrhea, and other intercurrent illnesses raise the body’s demand for glucocorticoids. Without a temporary increase in replacement hydrocortisone, the patient risks hypotension, hypoglycemia, hyponatremia, and progression to adrenal crisis ^[1].

The Endocrine Society guideline recommends that patients with adrenal insufficiency be educated to double or triple their usual oral glucocorticoid dose during febrile illness, depending on the severity of the stressor ^[1]. The specific instruction in this scenario—doubling each dose for fever of 38 °C or higher—is consistent with that framework.

Why the afternoon dose is also doubled
The patient’s fever is assumed to still be present when the afternoon dose is due. The sick-day rule applies to every scheduled dose while the qualifying stressor persists. The goal is to maintain a higher but still physiologically patterned cortisol level throughout the day, not to give one large morning dose and then return to baseline.

If the fever resolves before the afternoon dose, the patient would typically return to the usual 5 mg for that dose. However, the question explicitly states the fever is still present, so the afternoon dose is doubled to 10 mg.

Fludrocortisone is not part of the sick-day rule
Fludrocortisone replaces mineralocorticoid activity, primarily supporting sodium retention and potassium excretion. Short-term febrile illness does not require an increase in mineralocorticoid dosing because aldosterone secretion is not the primary stress-response hormone. In fact, excessive fludrocortisone during illness can contribute to fluid retention and hypertension. The sick-day plan therefore modifies only hydrocortisone ^[1].

Clinical reasoning for licensure exams
Sick-day dosing questions test whether the examinee can apply a written patient-specific plan rather than defaulting to a generic “stress dose.” The calculation steps are:

Step	Action	Result
Usual morning dose	15 mg	Doubled to 30 mg
Usual afternoon dose	5 mg	Doubled to 10 mg
Total today	30 mg + 10 mg	40 mg
Fludrocortisone	No change	0.1 mg daily

Key point! A history of pulmonary tuberculosis is relevant because tuberculosis is a common cause of primary adrenal insufficiency worldwide, but it does not alter the sick-day hydrocortisone calculation.

When to escalate beyond doubling
The doubling rule applies to mild-to-moderate febrile illness in a patient who can take oral medication and maintain hydration. If vomiting, severe diarrhea, altered mental status, or hypotension develops, oral dosing is unreliable and the patient needs parenteral hydrocortisone, typically 100 mg IV/IM immediately, followed by emergency care ^[1]. The current patient has none of these red-flag features.

Patient education and self-management are central to preventing adrenal crisis. Studies of patients using daily diaries show that timely dose adjustment during intercurrent illness reduces the risk of crisis, but adherence to sick-day rules varies and requires repeated reinforcement . Variability in how centers define and manage sick-day episodes also highlights the importance of giving each patient a clear, individualized written plan .

The correct total hydrocortisone dose for today is 40 mg, achieved by doubling each scheduled dose while the fever persists, with no change to fludrocortisone.